A nationwide hunt is on for the winners of almost 900,000 unclaimed premium bond prizes worth more than £44m. They include two six-figure wins and what could well be the UK's oldest unclaimed prize: £25 won by a man from South Yorkshire in 1957.

National Savings and Investments (NS&I) said it was looking for the winners of more than 898,000 premium bond prizes. There are a pair of £100,000 prizes waiting to be claimed, won by women in London and Greater Manchester in February 2007 and September 2010 respectively.

Another woman, last known to be living in Kent, has not claimed the £50,000 she scooped in November 2007, while two men from London and the West Midlands each have £25,000 with their name on it.

There is no time limit for claiming a premium bond win; each prize is held until the rightful winner can be tracked down. As a result there are prizes dating back several decades. The oldest is from November 1957 when a man living in South Yorkshire scooped the then-impressive sum of £25. There are several other prizes ranging from £25 to £100 dating back to 1960.

Some of these winners may be dead. However, an NS&I spokesman said that typically, if someone has died, the prize would go to their estate.

In many cases the unclaimed prizes have been left sitting in NS&I's system because the winners have moved house and failed to pass on their new address. Some people will have forgotten they had premium bonds – for example, if they were bought for them when they were a child.

The data shows that you don't need to have thousands of pounds of bonds to win a decent sum: the £100,000 winner from London has just £25 invested.

More than a third of the UK population has invested in excess of £45bn in premium bonds, with every eligible bond entered into the monthly prize draw. Investors forgo interest to have the chance to win tax-free cash.

Holders can reduce the chances of a prize being unclaimed by managing their bonds online or opting to have any winnings paid directly into their bank accounts, with notification of the win by email. To sign up holders should visit nsandi.com/register-our-online-service.

There is also a premium bonds prize checker on the home page of the NS&I website – customers simply need to enter their bond numbers into the search facility.